Actually the 420 is one of the biggest good SIBS available with air floor. I considered the 420 to be more roomy than the 380 and more seaworthy also. Its a good boat, had a tohatsu 25 on it. It was very seaworthy for a sib, did also a few long trips on the coast without any issues. At first tried to inflate it each time, than had it on the roof(little too big for that even that i did mad a cradle for it). Eventually purchased a small trailer, that's the only way to go in my opinion with a 25 hp(even tough it was light at 54 kg), launching is so much easier.
However the smaller kids was little scared, so upgraded to a SR 5.4. Now even the smallest doters complains if going too slow( less than 20 knots) or if there is not waves enough..
I sold the engine and trailer, consider selling the 420, also but haven't decided yet.